Circle of willis

The blood supply to the brain enters through the internal carotid arteries and the vertebral arteries, eventually giving rise to the circle of Willis.

Watch this
animation to see how blood flows to the brain and passes through the circle of Willis before being distributed through the cerebrum. The circle of Willis is a specialized arrangement of arteries that ensure constant perfusion of the cerebrum even in the event of a blockage of one of the arteries in the circle. The animation shows the normal direction of flow through the circle of Willis to the middle cerebral artery. Where would the blood come from if there were a blockage just posterior to the middle cerebral artery on the left?

Venous return

After passing through the CNS, blood returns to the circulation through a series of
dural sinuses and veins (
[link] ). The
superior sagittal sinus runs in the groove of the longitudinal fissure, where it absorbs CSF from the meninges. The superior sagittal sinus drains to the confluence of sinuses, along with the
occipital sinuses and
straight sinus , to then drain into the
transverse sinuses . The transverse sinuses connect to the
sigmoid sinuses , which then connect to the
jugular veins . From there, the blood continues toward the heart to be pumped to the lungs for reoxygenation.

Dural sinuses and veins

Blood drains from the brain through a series of sinuses that connect to the jugular veins.

Protective coverings of the brain and spinal cord

The outer surface of the CNS is covered by a series of membranes composed of connective tissue called the
meninges , which protect the brain. The
dura mater is a thick fibrous layer and a strong protective sheath over the entire brain and spinal cord. It is anchored to the inner surface of the cranium and vertebral cavity. The
arachnoid mater is a membrane of thin fibrous tissue that forms a loose sac around the CNS. Beneath the arachnoid is a thin, filamentous mesh called the
arachnoid trabeculae , which looks like a spider web, giving this layer its name. Directly adjacent to the surface of the CNS is the
pia mater , a thin fibrous membrane that follows the convolutions of gyri and sulci in the cerebral cortex and fits into other grooves and indentations (
[link] ).

Meningeal layers of superior sagittal sinus

The layers of the meninges in the longitudinal fissure of the superior sagittal sinus are shown, with the dura mater adjacent to the inner surface of the cranium, the pia mater adjacent to the surface of the brain, and the arachnoid and subarachnoid space between them. An arachnoid villus is shown emerging into the dural sinus to allow CSF to filter back into the blood for drainage.

Dura mater

Like a thick cap covering the brain, the dura mater is a tough outer covering. The name comes from the Latin for “tough mother” to represent its physically protective role. It encloses the entire CNS and the major blood vessels that enter the cranium and vertebral cavity. It is directly attached to the inner surface of the bones of the cranium and to the very end of the vertebral cavity.

Questions & Answers

what are the three types of blood stem and explanation how they form in steps

Homestatic regulations usually involves a (n) _ that detects a particular stimulus, and a(n) _that respond to the stimulus by communicating with a (n) _whose activity has an effect on the same stimulus.

Kaeze

A cell is producing proteins to be transported out of that cell. They will be processed on ribosomes that are